1. Field of the Invention
This invention relates to automatic lockout mechanisms for electrical equipment containers. More specifically, the invention relates to a system for preventing connection of electrical equipment within a cabinet unless the cabinet door is closed.
2. Description of the Related Art
Electrical equipment such as circuit breakers is typically housed within containers designed to prohibit access to the equipment at times when servicing the equipment would be unsafe. A circuit breaker for medium voltage applications will typically include male and female connectors for disconnecting the circuit breaker from the circuit prior to opening the circuit breaker""s container. Additionally, it is generally considered desirable to house such circuit breakers within an arc resistant container. To qualify as arc resistant, the door of the circuit breaker must be closed before the circuit breaker can be connected.
One example of a system for preventing access to a fuse box while the fuses are connected to the circuit is described in U.S. Pat. No. 5,757,260, issued to J. E. Smith et al. on May 26, 1998. This patent describes a pivoting rod blocking rotation of the door""s handle when the box containing the fuses is not fully retracted from the circuit. When the box if fully retracted, a pin on the carriage roller engages a camming surface on the rod, disengaging the rod from the door handle mechanism and permitting the door to be opened. Additionally, a slider prevents access to the threaded rod of the levering in mechanism when the door""s handle is rotated away from the locked position, thereby securing the carriage in the retracted position. An interlock acting on the carriage itself, instead of the levering in mechanism, may exhibit greater reliability.
Therefore, there is a need for an automatically operating interlock for electrical cabinets wherein the lockout mechanism is controlled by the position of the door itself instead of the door handle. Additionally, there is a need for an interlock mechanism that is simpler, easier to manufacture, and more reliable than presently available interlock systems.
The present invention is an automatically operating interlock for electrical cabinets, such as arc resistant circuit breaker cabinets. The interlock prevents connecting the circuit breaker or other electrical equipment within the cabinet unless the cabinet door is closed.
A typical circuit breaker for medium voltage applications is mounted on a carriage that is movable between a forward, disengaged position and a rearward, engaged position within the cabinet containing the circuit breaker. At least one pair of quick disconnects terminating in finger clusters protrudes from the rear of the circuit breaker, being dimensioned and configured to engage a pair of stabs at the rear of the circuit breaker""s cabinet when the circuit breaker is in the rearward position, thereby connecting the circuit breaker to the protected circuit. A typical medium voltage circuit breaker will use three pairs of mating stab/quick disconnect combinations. When the circuit breaker is moved to its forward position, the finger clusters are withdrawn from the quick disconnects, thereby disconnecting the circuit breaker from the circuit.
Moving the circuit breaker from one position to the other is accomplished by means of a threaded rod extending from the front to the rear of the cabinet. A levering in block engages the threaded rod so that rotation of the threaded rod pushes the levering in block either forward or rearward. The levering in block is secured to the carriage, so that rotation of the threaded rod thereby moves the carriage forward or backward. This process is known as levering in.
The interlock includes a spring-biased brake bar controlling the position of a pivotally mounted brake. The brake bar extends from the cabinet door to a position adjacent one of the wheels of the circuit breaker when the circuit breaker is in its forward, disconnected position. The rear end of the brake bar is pivotally secured to the brake. The brake is in turn pivotally secured to the cabinet floor, also adjacent to the circuit breaker""s wheel when the circuit breaker is in the forward position. The brake bar is biased to pull the brake against the wheel, thereby preventing movement of the circuit breaker. The front end of the brake bar is dimensioned and configured to abut the cabinet door when the door is closed. Closing the cabinet door pushes the brake bar rearward, thereby rotating the brake away from the wheel. The circuit breaker may then be moved from its forward, disconnected position to the rearward, connected position using the normal levering in procedure.
It is therefore an aspect of the present invention to provide an automatically operating interlock for electrical cabinets, preventing equipment within the cabinet from moving from a forward, disconnected position to a rearward, connected position unless the cabinet door is closed.
It is another aspect of the present invention to provide an automatically operating interlock for electrical cabinets that is actuated by the position of the cabinet door.
It is a further aspect of the present invention to provide an automatically operating interlock locking the rotation of the rollers for the equipment within the cabinet unless the cabinet door is closed.
It is another aspect of the present invention to provide a brake that is biased towards the rollers of electrical equipment within a cabinet unless the cabinet door is closed.
It is another aspect of the present invention to provide an automatically operating interlock mechanism for electrical cabinets including a spring biased brake bar controlled by the position of the cabinet door, and controlling the position of a brake.
It is a further aspect of the present invention to provide an automatically operating interlock that is simpler, more reliable, and easier to manufacture than other interlocks.